Adhesive filled with surface-treated chalk and soot

ABSTRACT

The invention relates to an adhesive composition containing a special silane cross-linking polymer and fine-particle coated calcium carbonate and soot. 20 to 50 ml of fine-particle coated calcium carbonate and soot are provided for every 100 g of polymer, and the volume ratio of fine-particle coated calcium carbonate and soot is between 70:30 and 30:70. The inventive adhesive composition is characterized by having good mechanical properties, a high electrical volume resistance and a good applicability.

REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 10/476,525filed Nov. 3, 2003, which in turn is a National Stage of InternationalApplication No. PCT/IB02/01247, filed Apr. 18, 2002, which claims thepriority benefit of European patent application no. 01 111 158.0, whichwas filed May 10, 2001 and whose entire disclosure content is herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates to filled adhesives, especially filledsilane-crosslinking adhesives.

PRIOR ART

Polyurethane polymers have long been known as especially suitablematerials for adhesive applications requiring high flexibility inconjunction with good strengths. One-component systems, in whichisocyanate end groups of the polyurethane polymer react with atmosphericmoisture to crosslink the polymer, have the advantage of simpleapplicability, since they require no metering of the second componentand no mixing operation. Systems of this kind find widespreadapplication as adhesives and sealants in industry and in construction. Afurther development of these polyurethane polymers involves replacingthe isocyanate functional groups by silane groups, which likewisecrosslink with atmospheric moisture to form Si—O—Si bonds. Thepreparation of silane-crosslinking polyurethane polymers by reaction ofthe terminal isocyanate groups with mercapto-functional oramino-functional silanes is described for example in U.S. Pat. No.3,632,557 (Union Carbide) and U.S. Pat. No. 5,364,955 (Bayer). U.S. Pat.No. 3,632,557 (Union Carbide) describes the preparation ofsilane-crosslinking organic polymers by reacting terminal isocyanategroups of polyurethane prepolymers with mercapto-functional oramino-functional silanes. These polymers may comprise, inter alia, afiller. Neither calcium carbonate nor soot are listed as examples.

On the basis of said patent it is indeed possible to preparesilane-crosslinking polyurethane adhesives and sealants, but themechanical values thereby achievable for formulations having rawmaterials costs that are in tune with the market range within the orderof magnitude of 1.5 MPa tensile strength and 150% elongation at break,which is inadequate for use as an adhesive in the automobile industry.

U.S. Pat. No. 5,364,955 (Bayer) describes, for the preparation ofsilane-crosslinking polyurethane polymers, special secondaryaminosilanes (aspartic ester derivatives) which are attached topolyurethane prepolymers having isocyanate end groups. Thesilane-terminal polymers can be used for formulating sealing materials.Indications of especially suitable fillers for achieving specialproperties are not mentioned.

The advantage of crosslinking via silane groups is that, on the onehand, crosslinking is not accompanied by the formation of any CO₂, whichunder certain circumstances can lead to disruptive bubbles in theadhesive, and that, on the other hand, the user does not come intocontact with monomeric isocyanates, which are a potential health hazard.

In addition to these documents which are unspecific as regards thefillers there are already works which deal with the attaining of specialproperties through the use of specific fillers.

U.S. Pat. No. 6,001,946 (Witco) describes more or less the samesilane-terminal polyurethane prepolymers, based on aspartic esterderivatives of amino-functional silanes, as U.S. Pat. No. 5,364,955.Reinforcing fillers listed include fumed silica, precipitated silica,and calcium carbonate, with treated calcium carbonate having a particlesize of from 0.07 to 4 microns particle size being referred to as apreferred filler. These fillers can be used alone or as a fillercombination. As a preferred quantity of filler mention is made of from80 to 150 parts per 100 parts of polymer. On the basis of that patent itis possible to achieve adhesives having tensile strengths ofapproximately 1.5 MPa with approximately 300% elongation. Adhesives ofthis kind are not strong enough for use in the automobile industry.

EP 0 676 403 (Witco) describes silane-terminal polyurethane polymerscontaining arylamino-functional silanes. Sealants based on thesepolymers are said to have higher elongation, higher flexibility, and alower elasticity modulus than the prior art at that time. Described aspreferred calcium carbonate fillers are treated types having particlesizes of from 0.05 to 10 microns in an amount of up to 100 parts per 100parts of polymer. On the basis of that patent it is possible to achieveadhesives having tensile strengths of approximately 2.8 MPa at 300%elongation. This tensile strength is still too low for application inthe automobile industry. Additionally it has been found thatsilane-crosslinking polyurethane polymers which comprise phenyl-aminosilane have a poor aging stability in the cured state under hot storage.

U.S. Pat. No. 5,703,146 (Kaneka) describes sealants composed of 100parts of silane-terminal oxypropylene polymer with a narrow molecularweight distribution, from 100 to 200 parts of calcium carbonate with aparticle size of not more than 0.5 micron, and surface-treated with afatty acid, and a number of further additions. The polymer has afraction of 15-35% in the overall composition. Through the combinationof the polymer having the narrow molecular weight distribution and hencelow viscosity with the fine-particle coated calcium carbonate stabilityis obtained adequately in combination with effective extrudibility, butsufficiently high tensile strengths are not obtained.

U.S. Pat. No. 4,222,925 (Inmont Corporation) describes an adhesive witha rapid curing rate and high strength, which is used in combination witha primer in automobile engineering to glue in windshields. The adhesiveis composed of a silane-terminal polyurethane polymer (prepared asdescribed in U.S. Pat. No. 3,632,557), a special amino-functionalsilane, and soot with a water content of not more than 0.05%. Theaddition of dried soot is said significantly to increase the mechanicalstrength of the adhesive. General indications of the amount of soot usedare absent, though example 2 discloses the use of 35 parts of soot per100 parts of polymer, which leads to very high mechanical values. Anadhesive formulation with a total fraction of 73% polymer in theformulation is too expensive, however, for a utility in tune withpractice.

WO 99/55755 (Essex) describes a method of gluing windows into astructure. The adhesive used is based on a silane-terminal oxyalkylenepolymer, a silane-terminal polyurethane polymer, or similarsilane-terminal systems. The polymer preferably has a fraction in theoverall composition of the adhesive of from 45 to 85%, contains a tincatalyst in a preferred amount of from 0.1 to 0.4%, a specialamino-functional silane and other additives. Soot, calcium carbonate,and other reinforcing fillers are listed as possible additives, withpreference being given to soot as the sole reinforcing filler used. Anamount of reinforcing filler of from 20 to 33%, based on the overalladhesive composition, is preferred, and compositions having tensilestrengths of up to 1028 psi (=7.1 MPa) are disclosed. As a consequenceof the high soot fraction in the adhesive it is impossible to achieve,with these adhesives, the high electrical volume resistance required foradhesive bonds in the automobile industry.

It is also already known to use both fine-particle coated calciumcarbonate and soot as an addition to silane-crosslinking polymers.

EP 0 819 749 (Simson) describes silane-crosslinking adhesives andsealants with high electrical resistance which are suitable forindustrial applications, such as the gluing in of auto windshields, or,in particular, as an adhesive and sealant for electrical appliances.These adhesives and sealants must include the following components:silane-terminal polymer, crosslinking catalyst, dryer, adhesionpromoter, and rheology controller, it being possible for from 25% to 55%of the composition to be in the form of a calcium carbonate filler. Whenprecipitated calcium carbonate grades coated with fatty acid are used,the viscosity of the composition is said to be increased, and thestability and—given the choice of a mixture of precipitated andunprecipitated calcium carbonate—the mechanical strength are said to beimproved. Soot, in an amount of from 0.2 to 5% based on the overallcomposition, is mentioned as a pigment.

EP 0 931 800 (Witco Corp.) describes sealants having improved mechanicalvalues, good curing rate, low surface tack and not excessively highviscosity. They are based on a silane-terminal polyurethane prepolymerwhich is prepared by reacting an OH-terminal polyurethane prepolymerwith an isocyanate-functional silane. Possible reinforcing fillersmentioned include fumed silica, precipitated silica, and calciumcarbonate, with soot being proposed as the principal filler in order tobring about even further reinforcement. Treated calcium carbonateshaving particle sizes of from 0.07 to 4 microns are preferred fillers.The fillers can be used alone or in combination, with the statedpreferred amount of filler being from 80 to 150 parts per 100 parts ofpolymer. The maximum tensile strength achieved in the examples is 2.7MPa.

None of these documents reveals any indication as to what must be theconstruction of an adhesive composition based on a silane-terminatedpolymer in order to meet the requirements imposed in the automobileindustry. None of these documents suggests that, using a special type ofsilane-terminated polymers, namely special silane-crosslinkingpolyurethane prepolymers, there exists a range within which thesilane-crosslinking polyurethane prepolymers can be filled with acombination of fine-particle coated calcium carbonate and soot in such away as to provide the properties necessary for the preparation ofadhesives for the automobile industry. Owing to the high mechanicalloads of the adhesive layer, these properties are a high strength of theadhesive in combination with good flexibility and, in order to achievecorrosion-resistant adhesive bonding between different metals, a highelectrical volume resistance of the cured adhesive. More specificallythese properties are

a tensile strength of at least 4.5 MPa,

an elongation at break of at least 250%,

an electrical volume resistance of at least 10⁸ ohm cm, and

good applicability,

all in combination with

raw materials costs that are not too high.

A high electrical volume resistance is also important because anexcessive conductivity of the adhesive layer can cause disruptions tothe receiving of radio when rear screens with built-in aerials are gluedin.

A further prerequisite for an adhesive in tune with practice is its goodapplicability. In other words, the uncured adhesive must be able to beextruded from the cartridge with reasonable force in the case of repair.The extrusion force from the cartridge through an opening with adiameter of 5 mm ought not to exceed a level of 2 000 N.

Moreover, the raw materials costs of a silane-crosslinking polyurethaneadhesive in tune with practice must not exceed a certain limit.Formulations which have a high polymer fraction of 70% or more aretherefore not in tune with the market.

Meeting all of these requirements is not possible with asilane-crosslinking adhesive in accordance with the present state of theart.

Surprisingly it has been found that silane-crosslinking polyurethaneadhesives that meet the aforementioned requirements for the adhesivebonding of components in the automobile industry can be formulated bycombining a special, silane-crosslinking polyurethane polymer in adefined range with fine-particle coated calcium carbonate and soot.

Depiction of the invention The present invention accordingly providesadhesives able to meet the requirements specified above. Such adhesivesof the invention comprise the following three constituents:

a) silane-crosslinking polyurethane polymer constructed in accordancewith the following formula (I):

where R¹ stands for an alkyl group having 2 to 8 carbon atoms, linear orbranched,

R² stands for an alkyl radical having 1 to 8 carbon atoms,

R³ stands for an alkyl radical having 1 to 5 carbon atoms,

a stands for 0 or 1,

Z stands for a sulfur or an NR⁴, where R⁴ stands for a hydrogen atom oran organic radical, for example, an alkyl group or an aryl group having1 to 20 carbon atoms, or a compound having ester groups such as, forexample, a moiety of the formula (II)

where R⁵ stands for an alkyl group having 1 to 8 carbon atoms,

n denotes a number from 2 to 4,

and A stands for a radical of a polyurethane prepolymer with thefunctionality n,

b) fine-particle coated calcium carbonate, by which is meant fattyacid-treated calcium carbonates having a particle size of from 0.05 to 1micron, with a density of approximately 2.6-2.7 g/ml, and

c) soot, preference being given to grades having a large surface area,with a density of approximately 1.8 g/ml,

there being from 20 to 50 ml of fillers b)+c) per 100 g polymer a), andthe volume ratio of b) to c) being between 70/30 and 30/70.

Preferably A stands for a polyurethane radical obtainable by reactingcommercially customary polyols with an excess of commercially customarypolyisocyanates, the average molecular weight of A usually being in therange from 500 to 100 000 g/mol, and A containing at least n urethanegroups. In particular A denotes a radical of the formula (III)

where Q stands for an aromatic, aliphatic or cycloaliphatic radicalwhich represents in particular a polyisocyanate, with special preferencea commercially customary diisocyanate, following elimination of two ormore isocyanate groups, and

P stands for a radical which represents a polyoxyalkylene-polyol orpolyalkyldiene-polyol, in particular a commercially customary polyol,following elimination of at least two OH groups,

X denotes a radical of the formula (IV)

where m independently of one another denotes 0 to 5 and where

Q has the abovementioned definition and where

P₁=P or denotes P(X)_(u), with the proviso that not more than one P₁ isP(X)_(u) and where

u=1 or 2.

Where the abovementioned conditions are observed the resultant adhesivesare suitable for the sealing adhesive bonding of components whichconsist at least in part of metal, as in the automobile industry, forexample. The adhesives have good mechanical properties, a highelectrical volume resistance, good applicability and reasonable rawmaterials costs. They can be applied effectively (i.e., they have anextrusion force of not more than 2 000 N), they have a tensile strengthof at least 4.5 MPa, an elongation break of at least 250%, and they havean electrical volume resistance of at least 10⁸ ohm cm.

WAY(S) OF PERFORMING THE INVENTION

An essential constituent of the adhesive compositions of the inventionis the silane-crosslinking polyurethane polymer which is constructed inaccordance with the following formula (I):

where R¹ stands for an alkyl group having 2 to 8 carbon atoms, linear orbranched,

R² stands for an alkyl radical having 1 to 8 carbon atoms,

R³ stands for an alkyl radical having 1 to 5 carbon atoms,

a stands for 0 or 1,

Z stands for a sulfur or an NR⁴, where R⁴ stands for a hydrogen atom oran organic radical, for example, an alkyl group or an aryl group having1 to 20 carbon atoms, or a compound having ester groups such as, forexample, a moiety of the formula (II)

where R⁵ stands for an alkyl group having 1 to 8 carbon atoms,

n denotes a number from 2 to 4,

and A stands for a radical of a polyurethane prepolymer with thefunctionality n.

Preferably A stands for a polyurethane radical obtainable by reactingcommercially customary polyols with an excess of commercially customarypolyisocyanates, the average molecular weight of A usually being in therange from 500 to 100 000 g/mol, and A containing at least n urethanegroups. In particular A denotes a radical of the formula (III)

where Q stands for an aromatic, aliphatic or cycloaliphatic radicalwhich represents in particular a polyisocyanate, with special preferencea commercially customary diisocyanate, following elimination of two ormore isocyanate groups, and

P stands for a radical which represents a polyoxyalkylene-polyol orpolyalkyldiene-polyol, in particular a commercially customary polyol,following elimination of at least two OH groups,

X denotes a radical of the formula (IV)

where m independently of one another denotes 0 to 5 and where

Q has the abovementioned definition and where

P₁=P or denotes P(X)_(u), with the proviso that not more than one P₁ isP(X)_(u) and where

u=1 or 2.

In the preferred case of n=2 the radical A can be depicted by theformula (V):

where Q stands for a radical which represents a diisocyanate, inparticular a commercially customary diisocyanate, following eliminationof the two isocyanate groups and P stands for a radical which representsa polyol, in particular a commercially customary polyol, followingelimination of the two OH groups, and m=0 to 5.

Preferred polyisocyanates are diisocyanates. Examples that may bementioned include the following isocyanates, which are very well knownin polyurethane chemistry:

2,4- and 2,6-toluene diisocyanate, 4,4′- and 2,4′-diphenylmethanediisocyanate, isophorone diisocyanate, 2,2,4- and2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,6-hexamethylenediisocyanate, m- and p-tetramethylxylylene diisocyanate, the isomers of4,4′- or 2,4′-dicyclohexylmethane diisocyanate, polymers or oligomers ofthese isocyanates, and mixtures of two or more of the statedisocyanates.

Polyols which, following elimination of at least two OH groups, producethe radical P are preferably the following raw materials, which are verywell known in polyurethane chemistry, or mixtures thereof:

polyetherpolyols, which are the polymerization product of ethyleneoxide, propylene oxide or butylene oxide or mixtures thereof, orhydroxy-terminated polybutadiene polymers. The polyols generally have anOH functionality of from 1.8 to 3 and a molecular weight from 500 to 20000 g/mol. In addition to said polyols it is possible in the preparationto use compounds having two or more OH groups, as well, as chainextenders or crosslinkers, so that their radicals may likewisecontribute to P. Examples that may be mentioned include 1,4-butane dioland trimethylol propane.

The silane-terminated prepolymers used in accordance with the inventioncan be prepared by reacting, in a first step, polyols with an excess ofpolyisocyanate, to give a prepolymer having isocyanate end groups. Theseisocyanate end groups are subsequently reacted with an organofunctionalsilane containing an isocyanate-reactive group.

Suitable organofunctional silanes are compounds with the formula (VI)

where R¹, R², R³ and a have the definition described above and Y standsfor —SH or —NH₂ or —NHR⁴, and R⁴ likewise has the definition describedabove. Particularly suitable is an amino silane containing as R⁴ thefollowing moiety (II)

where R⁵ stands for an alkyl group having 1 to 8 carbon atoms.

Organofunctional silanes of this kind can be prepared from thecorresponding maleic or furmaric diester and an amino silane whereY=—NH₂ by means of an addition reaction across the double bond. Anexample that may be mentioned of an organofunctional silane compound ofthis kind is the one below, prepared from diethyl maleic andγ-aminopropyltrimethoxysilane:

As polyols it is possible to use the raw materials already mentionedabove as “suppliers” of the radical P, which are very well known inpolyurethane chemistry, or mixtures of such materials.

Suitable polyisocyanates for preparing such a prepolymer include thealiphatic, cycloaliphatic or aromatic isocyanates having at least twoisocyanate groups per molecule, likewise mentioned already above as“suppliers” of the radical Q.

The preparation can take place by reacting the polyol component and theisocyanate component by customary methods, e.g., at temperatures of from50 to 100° C., where appropriate using suitable catalysts, and employingthe isocyanate component in excess. The reaction product formed is theaforementioned polyurethane prepolymer having isocyanate end groups.This prepolymer is subsequently reacted with the isocyanate-reactiveorganofunctional silane described, and the aforementionedsilane-terminal polyurethane prepolymer is formed. The organofunctionalsilane is used stochiometrically or in a slight excess in relation tothe isocyanate groups.

Particularly suitable as the fine-particle coated calcium carbonatedescribed under b) are calcium carbonates which have been surface-coatedwith fatty acids, such as stearates, for example, and which have anaverage particle size of from 0.05 to 1 micron. The amount of organicsubstance ranges between 0.9 and 5% weight fractions. Examples of gradeswhich are especially suitable are Winnofil SP and Winnofil SPT from ICIor So-cal U1S2 from Solvay. The density of these materials is from about2.6 to 2.7 g/ml.

The soot specified under c) is preferably a grade having a large surfacearea and having a density of approximately 1.8 g/ml, All possible sootgrades are suitable, provided they have been dried before being mixedinto the prepolymer. In order to reduce the electrical conductivity itis possible to use fully or partly oxidized soot grades, these gradesbeing more expensive and therefore being usable only in restrictedform - in order to give a market-compatible product which is not tooexpensive.

So that even when using unoxidized soot it is possible to obtain aproduct which meets the required properties, referred to above, theproportions are important. Consequently there are preferably from 20 to50 ml of fillers b)+c) per 100 g of polymer a), and the volume ratio ofb) to c) is between 70/30 and 30/70.

Besides these components, which are necessarily present, the adhesive ofthe invention may comprise one or more of the following constituents:

Plasticizers, examples being organic esters, e.g., phthalates such asdioctyl phthalate or diisodecyl phthalate, adipates such as dioctyladipate, for example, polybutenes or other compounds which are notreactive toward silanes, solvents, further organic or inorganic fillerssuch as, for example, other calcium carbonates, kaolines, aluminas,silicas, fibers, e.g., of polyethylene, pigments, thickeners, e.g., ureacompounds or polyamide waxes, heat stabilizers or UV stabilizers,adhesive promoters, e.g., amino silanes or epoxy silanes, especiallyH₂N—(CH₂)₃—Si (OCH₃)₃, H₂N—(CH₂)₂—NH—(CH₂)₃—Si(OCH₃)₃ orNH—[(CH₂)₃—Si(OCH₃)₃]₂, dryers, vinyltrimethoxy silane for example,catalysts, amine compounds for example such as isophoronediamine orJeffamines, for example, or organotin compounds, such as dibutyltinlaurate, dibutyltin acetylacetonate for example, or other catalystscustomary in polyurethane chemistry, and also further substancesnormally used in polyurethane sealants and adhesives.

As compared with the silane-crosslinking polyurethane prepolymers theadhesives of the present invention have the advantage that they areisocyanate-free and, by virtue of the inventive combination of a specialsilane-crosslinking polyurethane prepolymer, soot, and fine-particlecoated calcium carbonate, are suitable for applications requiring at oneand the same time tensile strengths of more than 4.5 MPa, elongations atbreak of more than 250%, an electrical volume resistance of more than10⁸ ohm cm, and good applicability. Examples of such applications arethe sealing and adhesive bonding of metallic components, especiallyflexible adhesive bonding. The adhesives of the invention are therefore,on the one hand, suitable for the production of buses, trucks, and railvehicles, and, on the other hand, are even able to meet the requirementsimposed on assembly adhesives in the automobile industry.

The invention is illustrated below with reference to examples which arenot, however, intended in any way to restrict it.

EXAMPLES

Starting materials used: Polyol PPG 12000 Acclaim 12200 from BayerPlasticizer Diisodecyl phthalate, e.g. from BASF Fine-particle coatedSocal U1S2 from Solvay calcium carbonate Soot Printex 60 from DegussaHuls Catalyst solution 90 parts by weight diisodecyl phthalate 10 partsby weight dibutyltin dilaurate

Description of the Test Methods

The extrusion force was determined in aluminum cartridges having adiameter of 45 mm, the adhesive being pressed through an opening of 5 mmat the tip of the cartridge. Extrusion took place by means of a tensiletesting machine, with recording of the required force, at a rate of 60mm/min.

The tensile strength and the elongation at break were determined oncured films in a layer thickness of approximately 3 mm in accordancewith DIN 53504 (S2).

The electrical volume resistance was measured at 1 000 V on cured filmsin a layer thickness of approximately 3 mm in accordance with DIN 53482.

EXAMPLE 1

Diethyl N-(3-trimethoxysilylpropyl)aspartate (maleic ester aminosilaneadduct)

509.9 g γ-aminopropyltrimethoxysilane were introduced into a vessel.Subsequently 490.1 g of diethyl maleic were added slowly, dropwise, andwith thorough stirring at room temperature. The temperature rise, causedby the exothermic reaction, was arrested at 30° C. by cooling in awaterbath. The mixture was subsequently stirred at room temperature for8 hours until the reaction was at an end.

EXAMPLE 2

Silane-terminated Polyurethane Prepolymer

1 000 g of polyol PPG 12000, 78.7 g of isophorone diisocyanate, and 0.13g of dibutyltin dilaurate were heated to 90° C. with constant stirringand left at that temperature until the free isocyanate group contentreached a figure of 0.7%. Subsequently 63.2 g of diethylN-(3-trimethoxysilylpropyl)aspartate from example 1 were mixed in andthe mixture was stirred at 90° C. for approximately 4 hours until freeisocyanate could no longer be detected by means of IR spectroscopy.Subsequently 0.4 g of silane A-171 was mixed in in order to scavengeresidual moisture, and the prepolymer was cooled to room temperature andstored in the absence of moisture.

EXAMPLES 3 to 7

Inventive Adhesives

The ingredients of the individual examples were mixed homogeneously inthe order according to table 1 in a suitable vacuum mixer, e.g.,Planimax from Molteni. In a first step the prepolymer, the plasticizer,and the fillers were homogenized, and subsequently the additionalsilanes and the catalyst solution were mixed in. The finished adhesiveswere filled into airtight cartridges.

EXAMPLES 8 to 11

Adhesives Outside the Scope of the Invention

The preparation procedure is the same as for examples 3 to 7. TABLE 1Composition of the adhesives (parts by weight) Example: 3 4 5 6 7 8 9 1011 Prepolymer from example 2 100 100 100 100 100 100 100 100 100Plasticizer 35 35 35 35 35 35 35 35 35 Fine-particle coated 31.2 62.4 5241.6 78 104 78 26 0 calcium carbonate Soot 32.4 28.8 36 43.2 36 0 18 5472 Vinyltrimethoxysilane 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5N-β-(aminoethyl)-γ- 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5aminopropyltrimethoxysilane Catalyst solution 2.5 2.5 2.5 2.5 2.5 2.52.5 2.5 2.5

TABLE 2 Degree of filling of the adhesives per 100 g of polymer Example:3 4 5 6 7 8 9 10 11 Total 30 ml 40 ml 40 ml 40 ml 50 ml 40 ml 40 ml 40ml 40 ml filler volume Calcium 40/60 60/40 50/50 40/60 60/40 100/0 75/2525/75 0/100 carbon- ate/soot ratio (by volume) Inven- Yes Yes Yes YesYes No No No No tive compo- sition:

TABLE 3 Properties of the adhesives Example: 3 4 5 6 7 8 9 10 11Extrusion force 660 870 1100 1640 2000 240 510 3000 7000 [N] Tensilestrength 5.9 4.8 5.5 4.5 4.9 1.8 3.3 4.8 6.3 [MPa] Elongation at 300 280300 250 250 330 310 160 150 break [%] Electrical volume 4.3 × 10¹⁰ 3.1 ×10¹⁰ 2.7 × 10¹⁰ 1.2 × 10¹⁰ 3.0 × 10¹¹ 1.3 × 10¹¹ 1.3 × 10¹¹ 1.4 × 10⁷3.2 × 10⁵ resistance [ohm cm]

The inventive adhesives of examples 3 to 7 meet the required properties,i.e., they have a tensile strength of at least 4.5 MPa, an elongation atbreak of at least 250%, an electrical volume resistance of at least 10⁸ohm cm, an extrusion force of not more than 2 000 N.

The adhesives from examples 8 to 11, which lie outside the scope of theinvention, do not meet all of the required properties. Examples 8 and 9,which contain no soot or only a small fraction of soot, have inadequatetensile strength. Examples 10 and 11, which contain only a smallfraction of coated calcium carbonate or none at all, have an excessiveextrusion force, an inadequate elongation at break, and an electricalvolume resistance which is too low.

Whereas the present application describes preferred embodiments of theinvention, it should clearly be pointed out that the invention is notrestricted to these embodiments and may also be performed in other wayswithin the scope of the claims which follow.

1. An adhesive composition comprising at least one silane-crosslinkingpolymer, fine-particle coated calcium carbonate, and soot, characterizedin that a) the at least one silane-crosslinking polyurethane polymer isconstructed in accordance with the following formula (I):

where R¹ stands for an alkyl group having 2 to 8 carbon atoms, linear orbranched, R²stands for an alkyl radical having 1 to 8 carbon atoms, R³stands for an alkyl radical having 1 to 5 carbon atoms, a stands for 0or 1, Z stands for a sulfur or an NR⁴, where R⁴ stands for a hydrogenatom or an organic radical, for example, an alkyl group or an aryl grouphaving 1 to 20 carbon atoms, or a compound having ester groups such as,for example, a moiety of the formula (H)

where R⁵ stands for an alkyl group having 1 to 8 carbon atoms, n denotesa number from 2 to 4, and A stands for a radical of a polyurethaneprepolymer with the functionality n, b) the fine-particle coated calciumcarbonate, is a calcium carbonate coated with fatty acid, especiallystearate, and having a particle size of from 0.05 to 1 micron and adensity of approximately 2.6-2.7 g/ml, and c) the soot is soot with adensity of approximately 1.8 g/ml, in particular soot having a largesurface area, there being from 20 to 50 ml of fillers b)+c) per 100 gpolymer a), and the volume ratio of b) to c) being between 70/30 and30/70.
 2. The adhesive composition according to claim 1, characterizedin that A stands for a polyurethane radical obtainable by reactingcommercially customary polyols with an excess of commercially customarypolyisocyanates, the average molecular weight of A usually being in therange from 500 to 100 000 g/mol, and A containing at least n urethanegroups.
 3. The adhesive composition according to claim 1, characterizedin that A denotes a radical of the formula (III)

where Q stands for an aromatic, aliphatic or cycloaliphatic radicalwhich represents in particular a polyisocyanate, with special preferencea commercially customary diisocyanate, following elimination of two ormore isocyanate groups, and P stands for a radical which represents apolyoxyalkylene-polyol or polyalkyldiene-polyol, in particular acommercially customary polyol, following elimination of at least two OHgroups, X denotes a radical of the formula (IV)

where m independently of one another denotes 0 to 5 and where Q has theabovementioned definition and where P₁=P or denotes P(X)_(u), with theproviso that not more than one P₁ is P(X)_(u) and where u=1 or 2, andwhere the average molecular weight of A is preferably in the range from500 to 100 000 g/mol,
 4. The adhesive according to claim 1,characterized in that the radical A has a funtionality n=2 and can bedepicted by formula (V)

where Q stands for a radical which represents an aliphatic,cycloaliphatic or aromatic polyisocyanate following elimination of atleast 2 isocyanate groups, in particular a dissocyanate, followingelimination of both isocyanate groups, and P stands for a radical whichrepresents a polyalkyldiene- or polyoxyalkylene-polyol followingelimination of at least 2 of OH groups, in particular a diol, followingelimination of both OH groups, and m=0 to
 5. 5. The adhesive accordingto claim 1, characterized in that Q is the radical which remainsfollowing elimination of 2 isocyanate groups from one of the isocyanatesfrom the following group: 2,4- and 2,6-toluene diisocyanate, 4,4′- and2,4′-diphenylmethane diisocyanate, isophorone diisocyanate, 2,2,4- and2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,6-hexamethylenediisocyanate, m- and p-tetramethylxylylene diisocyanate, the isomers of4,4′- or 2,4′-dicyclohexylmethane diisocyanate, polymers or oligomers ofthese isocyanates, and mixtures of two or more of the statedisocyanates.
 6. The adhesive according to claim 1, characterized in thatP is the radical that remains following the elimination of at least twoOH groups from a polyol from the following group: polyetherpolyols,which are the polymerization product of ethylene oxide, propylene oxideor butylene oxide or mixtures thereof, or hydroxy-terminatedpolybutadiene polymers, especially polyols having an OH functionality offrom 1.8 to 3 and a molecular weight from 500 to 20 000 g/mol.
 7. Theadhesive according to claim 1, characterized in that it furthercomprises one or more of the following constituents: plasticizers,especially organic esters and polybutenes, solvents, further organic orinorganic fillers, such as other calcium carbonates, kaolines, aluminas,silicas, fibers, pigments, thickeners, heat stabilizers or UVstabilizers, adhesion promoters, dryers, catalysts.
 8. A process forpreparing an adhesive according to claim 1, characterized in that the atleast one silane-terminated polyurethane prepolymer is prepared byreacting - in a first step -polyols with an excess of polyisocyanate togive a prepolymer having isocyanate end groups and in that theseisocyanate end groups are subsequently reacted with at least oneorganofunctional silane containing an isocyanate-reactive group,whereupon the prepolymer thus obtained is subsequently mixed in theabsence of moisture with soot dried beforehand and with fine-particlecoated calcium carbonate dried beforehand.
 9. The process according toclaim 8, characterized in that the organofunctional silane is a compoundwith the formula (VI)

where R¹, R², R³ and a have a definition described above and Y standsfor —SH or —NH₂ or —NHR⁴, and R⁴ likewise has the definition describedabove, especially aminosilane containing as R⁴ the following moiety

where R⁵ stands for an alkyl group having 1 to 8 carbon atoms.
 10. Theprocess according to claim 8, characterized in that the polyol- and theisocyanate are reacted at temperatures of from 50 to 100° C., usingwhere appropriate suitable catalysts as well, the isocyanate componentbeing employed in excess, and where this polyurethane prepolymer havingisocyanate end groups is subsequently reacted with the organofunctionalsilanes stoichiometrically or in a slight excess.